Arc plasma generator



United States Patent O 3,182,176 ARC PLASMA GENERATOR Edgar A. Bunt, Kensington, and Herman L. Olsen, Derwood, Md., assignors to the United States of America as represented by the Secretary of the Navy Filed Dec. 10, *1962, Ser. No. 243,682 7 Claims. (Cl. 219-121) This invention relates Ygenerally to arc plasma generators; more particularly, it relates to an improved arc plasma generator for continuously producing a high pressure, high temperature plasma discharge.

For purposes of this invention the term plasma discharge is defined .as a partially ionized, gaseous-like mass derived by passing air or a similar substance through a high energy electric arc. The plasma discharge is therefore a collection of neutral particles, ionized particles, and free electrons, all of which are free to move and have mutual collisions. The temperature of the discharge produced by the device of the invention is of the same order as the measured temperature at the surface of the sun, or about 10,000 F.

Numerous applications have been found for the plasma discharge of an arc plasma generator, including the testing of materials, cutting, welding, metal spraying, chemical processing, and as a heat source for wind tunnel facilities capable of simulating hypersonic ight.

It is the principal object of this invention to provide an arc plasma generator employing concentrically disposed, circular electrodes, and being so constructed as to operate at several megawatts of power and under very large gas pressures to produce a continuous plasma discharge.

A further object of the invention is to provide an arc plasma generator so constructed that the electrodes thereof may be easily changed and so that the spacing between the electrodes may be varied.

It is also an object of the invention to provide an arc plasma generator in which cooling means are provided to cool all surfaces exposed to direct radiation emanating from the plasma discharge and to high temperature gases.

Another object of the invention is to provide an arc plasma generator so constructed that the operation thereof may be observed both visually and by instruments.

Yet another object of the invention is to provide an arc plasma generator so constructed that it may be easily disassembled for servicing.

A still further object of the invention is to provide an arc plasma generator in which all electrical insulation elements are so positioned that radiation emanating from the plasma discharge will not fall directly thereon.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein the single ligure is an axial section of the are plasma generator of the invention.

The arc plasma generator of the invention comprises a cylindrical pressure vessel within which are disposed outer and inner concentrically arranged electrode supports, insulation elements being interposed between the outer electrode and the pressure vessel and between the inner and outer electrodes to electrically insulate these elements from one another. Attached to each electrode support is one of a pair of annular, generally semi-circular in cross-section, electrodes, the two electrodes being disposed concentrically and in opposing relationship in a plane transverse to the longitudinal axis of the pressure vessel. A stilling chamber is defined by the pressure vessel and extends forwardly of the electrodes to a front retainer plate, an exit nozzle orifice being disposed cen- ICC trally of said plate. The surfaces of the pressure vessel, the electrode supports, the electrodes, the retainer plate and the exit nozzle which are exposed to the plasma discharge generated by the device are all cooled by the flow of a liquid coolant, and the insulation elements are so positioned that, in so far as is possible, no direct radiation emanating from the plasma will fall thereon.

In operation, electricity is supplied to the inner electrode and a gas under pressure is admitted into the rear end of the generator. An arc is caused to be formed between the electrodes, the same being rotated around the peripheries of the electrodes by a rotating magnetic field created by a lield coil disposed about the exterior of the pressure vessel. The gas admitted to the device flows through the arc, is partially ionized and converted into plasma thereby, and thence flows out of the stilling chamber through the exit nozzle orifice.

Referring now to the drawing, a cylindrical pressure vessel is indicated at 2. The interior cylindrical surface of the vessel 2 has therein a rear circumferential groove 4 and a front circumferential groove 6, an inwardly projecting annular flange 8 being positioned between said rear and front grooves near the rear groove. A disc 10, constructed of insulation material and having a central threaded opening therein, is disposed within the vessel 2 and abuts against flange 8, said insulation disc being secured in position by a retainer plate 12 anda snap ring 14, the ring 14 being received Within the groove 4. The insulation disc 10, as well as the insulation elements yet to be described, may be made of any suitable material, such as a phenolic resin or a micaceous substance.

The insulation disc 10 has an annular recess in the front face thereof, the outer wall of said recess being threaded for reception of the lthreaded rear end of an outer electrode support 16. The rear end face of -the electrode support 16 preferably has an annular groove therein (not shown for purposes of clarity) for receiving an O-ring seal to thereby seal the support 16 relative to the insulation disc 10. Attached to the outer electrode support 16 by a plurality of circumferentially-spaced screws 18 is a water and air manifold 20, an externally threaded insulating sleeve 22 being interposed between the manifold 20 and insulation disc 10 and being screwed into the threaded opening within the latter.

The water and air manifold 20 and the outer electrode support 16 have aligned, communicating central openings 24 and 26, respectively, therein. The opening 24 defines an inturned lip at `its forward end, and contains a cylindrical insulation sleeve 28 having a simila-r inturned lip at its forward end. The opening 26 has an enlarged portion 30 at its forward end, the portion of the opening 26 immediately to the rear of said enlarged portion being threaded. An insulating sleeve 32 is fitted within opening 26 and is of a length sutiicient to project in-to opening 24 and to abut the insulating sleeve 28. The sleeve 32 has an intermediate enlarged portion of a size to tit within enlarged portion 30 of opening 26, and an enlarged cylindrical forward portion 34. The sleeve 32 also has threads on the exterior surface thereof positioned to engage the threaded portion of opening 26, and an O-ring seal (not shown for purposes of clarity) is positioned in a groove on the end portion thereof for sealing engagement with the support 16.

The front portion of an inner electrode water manifold 36 is telescopically received within the bore of the sleeve 28, the forward end of said manifold abutting against the inturned lip at the forward end of said sleeve. The manifold 36 has a central bore 38 extending therethrough, said bore being enlarged near the forward end of said manifold to form a socket for slidably receiving the rear end of an inner electrode support 40, an O-ring seal (not shown) being disposed in a peripheral groove on said inner support 40 for sealing the same with respect to the axially extending wall of said socket. The inner support 40 extends through the opening defined by the inturned lip at the forward end of sleeve 28, through the interior of sleeve 32, and projects into the interior of the device, the forward end thereof having an enlarged head portion 42 thereon. The head portion 42 defines a radial end wall which abuts against the front end face of sleeve 32, the latter preferably having an annular groove therein (not shown) for receiving an O-ring seal. The sleeve 32 and the inner support 40 are connected by mating screw threads 44, and the support 40 has a central bore 46 extending therethrough which terminates at the forward end of the support in an enlarged socket 4S.

The bores 38 and 46 are in alignment and are of the same diameter, whereby a `tubular electrical conductor 50 may be positioned therewithin. The forward end of said conductor has a peripheral flange thereon of a size to fit snugly within the socket 48 in inner support 40, and the rear end of said conductor is of a length Ito project a substantial distance beyond the rear end of manifold 36. Screw threads are provided on the conductor 50 near the rear end of manifold 36, and a lock nut 52 is screwed thereon into abutment with the end face of said manifold. Thus, the manifold 36 and the inner support 40 are clamped together between the peripheral flange on the conduit 50 and the lock nut 52.

The outer support 16 has a front end face thereon in which is formed an annular groove 54. An integral tubular portion 56 extends forwardly of said front end face, there being an annular socket 58 in the end face of said tubular section. A peripheral groove 60 is positioned in the exterior surface of said support 16 just forwardly of the threaded rear end thereof. The portion of the support 16 extending forwardly of the groove 60 is of a uniform diameter somewhat smaller than the diameter of the threaded rear end, and the surface thereof carries a large number of circumferentially-spaced splines 62 thereon. An outer tubular water jacket 64 is fitted about the support 16 and is secured thereto, as by welding, the water jacket having an inwardly directed flange near its front end whereby to form a socket 66 in the end face thereof.

An inner water jacket 68 is positioned within tubular portion 56 and includes an axially extending tubular portion and a radially extending flange portion 70. A plurality of integral, circumferentially-spaced splines 72 are disposed on the outer surface of the tubular portion of said jacket 68, and a plurality of rearwardly projecting fins 74 are disposed on the rear side of flange 70. The fins 74 project a distance suflicient so that when the same are in abutment with the bottom wall of groove 54 the front face of flange 70 will be flush with the radial face containing said groove, said Water jacket being secured to the support 16, as by welding. The internal, front end of the inner jacket 68 is threaded, and an inwardly projecting flange adjacent said threads carries an O-ring seal 76 in an annular groove in the end face thereof.

Attached to the inner jacket 68 by the threads at the forward end thereof is an outer electrode 78, said electrode being an integral, annular, hollow element having a thread-bearing radially outwardly directed rear wall, a semi-circular, inwardly directed electrode surface 80 and a radially outwardly directed front wall. The rear wall abuts the O-ring 76, and the outer periphery of the front wall fits into the socket 66. Disposed within the outer electrode 78 is a circular water guide 82, said guide having circumferentially-spaced ribs 84 and S6 on the front and rear faces thereof, respectively. The water guide 82 is made in two or more segments, to enable the same lto be placed in the position shown, and the outer periphery has a circumferential notch therein at the rear face thereof a size to fit within socket 58.

The enlarged head 42 of inner electrode support 40 includes a large cylindrical portion and an intermediate cylindrical portion connected by a frusto-conical portion 88. The large portion has a peripheral groove medially thereof, and circumferentially-spaced splines 92 extend forwardly of said groove on said enlarged head portion. An inner electrode Water jacket 94 is fitted over said enlarged head, and is secured thereto, as by welding.

Mounted upon the forward end of conductor 50 and abutting against the flange thereon is an integral inner electrode 96, said electrode including a cylindrical mounting collar 98, a front radial wall, an outwardly directed, semi-circular in cross-section electrode surface 100, and a rear tapered wall 102, said rear wall having a cylindrical interior of a size to easily fit about the front end of water jacket 94. An 0-ring 104 is seated in a groove in the cylindrical interior of said rear wall, and frictionally engages the water jacket 94 to hold the electrode in position and to seal it relative to said jacket.

Disposed within the inner electrode is an annular water guide 106 having a central opening 108 extending therethrough, the rear portion of said opening being larger in diameter than the front portion thereof. The guide 106 has a notched rim 110 extending about its periphery and a plurality of ribs 112 on the front and rear faces thereof. The water guide 106 is made in several segments to facilitate assembly into the inner electrode, the segments being held in assembled position by a cylindrical collar 114. The exterior of collar 114 is shaped to correspond to the portions of opening 108, and the forward end thereof has a plurality of radial slots 116 therein. The collar rests upon the forward, relatively small in diameter, end of the inner electrode support 40.

The inner and outer electrode supports 40 and 16 are so positioned that the inner and outer electrode surfaces 100 and 80 are opposed in a plane transverse to the longitudinal axis of the device, the spacing between the annular surfaces being a matter determined from the given operating characteristics. The electrodes and their supports are so constructed that they may be fluid cooled during operation of the device, thereby enabling operation at exceedingly high temperatures. The cooling fluid distribution system will now be described.

The outer electrode support 16 has a plurality of circumferentially-spaced, elbow-shaped bores 118 therein, the outer radial ends of said bores communicating with annular groove 60. The other, or inner, ends of the bores 118 are positioned to confront a like plurality of bores 120 in manifold 20, the outer ends of the bores 120 being threaded for reception of conduits (not shown). The juncture between each of the mating bores 118 and 120 is sealed by an O-ring (not shown) disposed about said juncture and carried in an annular groove in the rear end face of support 16.

In operation, one-half of the bores 120 are connected to fluid supply lines and the other half to uid exhaust lines. Fluid then flows through the supply half of bores 118 and 120, groove 60, the space defined by the water jacket 64 and splines 62, the space defined by the inner wall of electrode 78, water guide 82 and ribs 84 and 86, the space defined by inner water jacket 68 and splines 72, and the space defined by flange 70, the walls of groove 54, and fins 74. The fluid then follows a reverse path and flows out of the device through the exhaust half of the bores 118 and 120.

The inner electrode and its support are cooled by fluid flowing through an inlet pipe 122 and port 124 into an annular chamber 126 in manifold 36. The inner support 40 has a plurality of circumferentially-spaced bores 127 which confront the chamber 126 at the interface between the support 40 and manifold 36. A radially directed p0rtion of each bore 127 conducts the fluid to annular groove 90, whence it flows through the space defined by splines 92 and water jacket 94, and the space defined by inner electrode 96, water guide 106, notched rim 110, ribs 112, and collar 114. The fluid then flows through the slots 116 in collar 114, through the space defined by the inner electrode collar 98 and collar 114, and into a plurality of circumferentially-spaced bores 128 in the support 68. The bores 128 confront a second annular chamber 130 in manifold 36, and fluid ows out of said annular chamber through port 132 and outlet pipe 134.

From the above it is seen that all exposed portions of the inner and outer electrodes and their supporting structure are cooled by the flow of a fluid coolant, the rate of cooling being largely dependent upon the fluid employed and the rate of its flow.

The interior of pressure vessel 2 is fitted with a cylindrical Water jacket 136 having a helical projection 138 extending over the major portion of the outer surface thereof. The jacket 136 is in abutment with flange 8, and has O-ring-bearing peripheral grooves 140 and 142 near the rear and forward ends, respectively, thereof, there being a peripheral manifold groove 144 on the jacket to the rear of the rear O-ring groove 140. Fluid is admitted through threaded ports 146 in the pressure vessel into the space defined by said pressure vessel, the Water jacket 136, and helical projection 138. Such uid serves to cool the water jacket, and then passes out of the device through threaded exit ports 148 in the forward end of the pressure vessel.

The water jacket 136 is maintained in position by a front retainer plate 150, which plate is in turn maintained in position by a `snap ring 152 positioned in the groove 6. The periphery of plate 150 has a reduced, intermediate cylindrical portion upon which the front end of jacket 136 rests, and a further reduced-in-diameter, rear cylindrical portion. A frusta-conical bore 154 is positioned centrally of the plate 150 and tapers downwardly in diameter from the rear of the plate to the front thereof. An annular socket 156 is formed in the plate around the rear end of tapered bore 154, and the plate around the periphery of the front end of said bore is chamfered. Disposed within the tapered bore is a nozzle body 158 having a frusto-conical bore therethrough and a plurality of ribs 160 on the outer .surface thereof, said ribs being of a shape to snugly fit Within bore 154 and socket 156.

A nozzle retainer plate 162 is attached to plate 150 by a plurality of circumferentially-spaced screws 164, and has a central bore 166 therein. The rear face of the plate 162 has an annular socket 168 therein which is in communication with bore 166, and which has a diameter substantially the same as the outer diameter of the chamfer at the end of bore 154. An orifice nozzle section 170 is disposed in bore 166 and has circumferentially-spaced ribs 172 thereon of a size to snugly fit within the socket 168. The orifice section 170 has a bore 174 therethrough, the rear portion of said bore being of a shape to form an extension of the frusto-conical interior of nozzle body 158. The forward portion of said bore 174 is defined by the front face of an integral circumferential flange portion 176 of the orifice section 170. The flange 176 lits snugly within bore 166, and is sealed thereto by an O-ring (not shown) in a peripheral groove in the wall defining said bore 166. The rear face of section 170 abuts the front face of nozzle body 158, the latter face having an O-ring seal (not shown) seated in an annular groove therein.

Fitting in abutment against the rear face of retainer plate 150 is a water guide plate 178, said plate 178 having a cylindrical projecting portion 180 which is telescopically received over the rear, reducedein-diameter portion of the periphery of said retainer plate. The cylindrical projecting portion is secured to the retainer flange by a plurality of radially-directed screws (not shown), and an O- ring seal (not shown) is carried in an annular groove on the reduced-in-diameter portion of plate 150 and seals said portion relative to the water jacket 136.

The water guide plate 178 has a central opening 182 therein which is shaped to form an entrance area into the nozzle body 158. An annular flange 184 surrounds the opening 182 and projects forwardly of the plate 178 into abutment with the rear face of the nozzle body 158, an O-ring seal (not shown) being disposed in an annular groove in the end face of said ange 184 to seal the plate 178 to the nozzle body. The plate 178 also has an inner ring of circumferentially-spaced ribs 186 and an outer ring of similarly spaced ribs 188 projecting therefrom, which ribs abut the rear end face of the retainer plate 150.

The retainer plate is provided with a pair of circumferentially-spaced, stepped-in-diameter observation bores 190. Disposed within one of said observation bores is a window 192 of, say, quartz. The other observation bore contains a pressure transducer 194. The number of observation bores employed is obviously a matter of design, the bores being positioned in axial alignment with the gap between the inner and outer electrode surfaces 80 and 100.

The water guide plate 178 is provided with a plurality of observation openings 196, one such opening being in alignment with each observation bore 190. An annular ange surrounds each observation opening 196 and extends forwardly into abutment with the rear Wall of retainer plate 150. The openings 196 are smaller in diameter than the enlarged portions of bores 190, and hence the annular flanges surrounding said openings serve to secure the elements 192 and 194, or any similar such elements, in position.

Because of the extreme operating temperature within the device of the invention, and because of the plasma flowing through the exit nozzle, it is necessary that all exposed surfaces of the front retainer plate and the nozzle be cooled. This cooling is accomplished by passing a coolant through cooling passages in said retainer plate in the manner now to be described.

A suitable coolant is admitted to the device through a plurality of threaded, circumferentially-spaced bores 198 within the plate 150, and thence flows radially inwardly through the space defined by the rear face of said plate 150, the front face of Water guide plate 178, the inner and outer spaced ribs 186 and 188, the cylindrical projection 180, annular ange 184, and the flanges surrounding openings 196. From said space the coolant flows into the space defined by the walls of annular socket 156, bore 154, and by the ribs and the outer surface of the nozzle body 158. Thereafter it flows into the space defined by the walls of annular socket 168 and bore 166, the ribs 172, the outer surface of nozzle section 174, and the ange 176, and thence out of plate 162 through a plurality of circumferentially-spaced, radially directed bores 200. The amount of heat conducted away by the coolant is dependent primarily upon the coolant employed and its rate of ow.

As mentioned hereinabove, plasma is generated in the device of the invention by passing a gas through an electrical arc or discharge. In the device such gas is admitted through a plurality of ports 202 in the manifold 20, said bores being in communication at their inner ends with an annular manifold groove 204. O-ring seals (not shown) are disposed in annular grooves in the rear face of the outer electrode support 16 radially inwardly and radially outwardly, respectively, of said manifold groove 204. A large plurality of bores 206 are disposed within the outer support 16, said bores 206 being positioned to confront manifold groove 204 and to communicate said groove with the annular space 208 between the inner and outer electrode supports. Thus, air admitted through the ports 202 may flow into manifold groove 204, through bores 206, and thence into the annular space 208.

In certain instances it is desirable to intermix a gas or other substance with the plasma before the same is discharged from the generator through the exit nozzle. To provide for such situations the conductor 50 has a bore 210 completely therethrough, said bore being threaded at its front and rear ends. A threaded plug 212 is normally screwed into the threaded front of the bore 210 to close the same. When a substance is to be injected into plasma generated by the device the plug 212 may be removed, andthe substance may be inserted into the stilling chamber 214 (which stilling chamber is defined as the area between the electrodes, the water guide plate 178, and water jacket 136) through the bore 210. When not required for injecting material into the generator, the bore 210 should have coolant introduced thereinto for cooling the plug 212 to thus prevent said plug from being eroded away.

Gas may also be injected into the stilling chamber 214 through ports 216 in the pressure vessel 2, which ports communicate with the manifold groove 144 in water jacket 136i. A plurality of circumferentially-spaced bores 218 communicate said groove 144 with an annular space 220 between the water jacket 64 and the water jacket 136. Gas injected into the ports 216 will iiow into groove 144, through bores 218 and space 220, and into the stilling chamber 214.

The bore 210 in the conductor 50 also provides a means for inserting an instrumented probe of any suitable type into the stilling chamber 214 for purposes of further observing the operation of the device.

In operation, the conductor 50 is connected by a connector clamp 222 to the negative pole of a source of direct current voltage and to ground. The outer electrode is connected to the positive terminal of the source, and an arc is caused to be formed between the opposing electrode surfaces 80 and 100. The arc may be established by any suitable means, one method being by initially extending a thin conductor between the electrode surfaces.

The arc would rapidly erode the electrode surfaces if permitted to remain in one area for more than a fraction of a second. Hence, a suitable magnetic coil (indicated by broken lines at 224) is disposed about the pressure vessel 2. Said coil is of a conventional type that establishes a very rapidly rotating magnetic eld, which field causes the arc discharge to rotate rapidly about the longitudinal central axis of the electrodes.

The ow of coolant into the ports 120, 124, 146 and 198 is established, and then a suitable gas is injected into space 208 in the manner hereinabove described` The gas ows through the arc, is partially ionized and converted into plasma thereby, and thence flows into stilling chamber 214, from which it flows out of the generator through the nozzle opening. The resultant plasma discharge may then be utilized for whatever purpose desired.

The arc plasma generator of the invention is so designed that all direct radiation emanating from the plasma will fall upon a surface cooled by the ow of coolant, the only surfaces not so cooled being the front face of insulation disc 10 and the cylindrical surface of the fort ward portion 34 of insulating sleeve 32. These latter two surfaces are so positioned relative to the electrodes and to the stilling chamber 214 that substantially no direct radiation from plasma will fall thereon, and hence these surfaces are protected from extreme temperatures norf mally created by the impingement on an object of such radiation; while a small degree of radiation may impinge on the insulation 10 because of the annular passageway 220, its effect is usually negligible.

It has been found that if the interior surface of water jacket 136 is plated or coated with a bright metal, say silver, the resultant reflective surface will further serve to reduce the heating effect of the impingement thereon of radiation.

It has also been found that the inner electrode 96 has a tendency to erode slightly because of the action thereon of the arc discharge, even if the arc is rapidly rotated. By constructing the electrode 96 of silver, material eroded therefrom will fall upon the inner surface of water jacket 136 and will help form a shiny deposit thereon, hence improving the radiation reflecting characteristics thereof. The reason for utilizing silver is that the oxide thereof formed from erosion by the arc is unstable at high temperatures; thus, in the presence of the high temperature arc the silver, not its oxide, is deposited on the surface of the vessel.

The arc plasma generator of the invention is designed to produce four megawatts at 600 volts, and will withstand gas pressures up to three thousand p.s.i. The resultant plasma discharge will possess a temperature in the vicinity of l0,000 F. In a typical construction the pressure vessel 2 and the rear and front retainer plates 12 and 150 will be of austenitic stainless steel, or other non-magnetic metal, the manifolds 20 and 36, plate 162, water guides 82 and 106, and collar 114 will be of brass, the water jackets, water guide plate 178, nozzle body 158, nozzle portion 170, the inner and outer electrode supports 40 and 16, and outer electrode 78 Will be of copper, and the inner electrode 96 will be of silver or nickel.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. An arc plasma generator, comprising a hollow cylindrical pressure vessel,

end walls closing said vessel at its opopsite ends,

an inner electrode support mounted concentrically of and extending through one of said end walls,

a generally cylindrical outer electrode support mounted concentrically of said inner electrode support and also extending through said one end wall,

insulation means disposed between said electrode supports,

an annular inner electrode supported on said inner electrode support,

an annular outer electrode supported on said outer electrode support concentrically about and radially spaced from said inner electrode, said electrodes being arranged in confronting relationship and said insulation means being disposed substantially out of view of an arc struck between said electrodes,

means for producing an arc between said electrodes,

nozzle means mounted centrally of the other of said end Walls, and

a coil disposed about said pressure vessel and arranged to create a rapidly rotating magnetic eld for causing an arc struck between the electrodes to rotate about the axis of said electrodes.

2. An arc plasma generator as recited in claim 1, wherein said electrodes have substantially identical longitudinal widths and wherein the confronting surfaces thereof are rounded.

3. An arc plasma generator as recited in claim 1, wherein said electrode supports, said electrodes, the inner cylindrical Wall of said pressure vehicle, and said other end wall are provided with channel means for passing a fluid coolant therethrough.

4. An arc plasma generator, comprising a hollow cylindrical pressure vessel,

detachably secured wall means closing said vessel at its opposite ends,

an inner electrode support mounted concentrically within said vessel and extending through one of said detachably secured wall means,

a generally cylindrical outer electrode support mounted concentrically with said pressure vessel about said inner electrode support, said outer electrode support extending through said one end wall and being radially spaced from both said pressure vessel and said inner electrode support,

an annular, generally semi-circular in cross-section inner electrode supported on said inner electrode support within said vessel,

an annular, generally semi-circular in cross-section outer electrode supported on said outer electrode support concentrically about and radially spaced from said inner electrode, the rounded, generally semicircular surfaces of said electrodes being disposed in confronting relationship and both of said electrodes having nearly identical widths,

rst insulation means disposed between said electrode supports,

second insulation means disposed between said outer electrode support and said one end wall, both said iirst and said second insulation means being disposed substantially out of view of an arc struck between said confronting electrode surfaces.

means for producing an arc between said electrodes,

nozzle means mounted centrally of the other of said end walls, and

a coil disposed about said pressure vessel in ythe region of said confronting electrode surfaces and arranged to create a rapidly rotating magnetic field for causing an arc struck between said confronting surfaces to rotate about the center of said concentrically disposed electrodes.

5. An arc plasma generator as recited in claim 4, wherein said electrode supports, said electrodes, the inner cylindrical wall of said pressure vessel, and said other end wall are provided with channel means for passing a fluid coolant therethrough.

6. An arc plasma generator as recited in claim 5, in-

cluding additionally 10 wherein the surface finish of the inner wall of said pressure vessel is relatively highly reective.

References Cited by the Examiner UNITED STATES PATENTS 2,768,279 10/56 Rava 219-75 3,004,137 10/61 Karlovi-tz 219-75 3,007,072 10/61 McGinn et al 313-231 3,048,73 6 8/62 Emmerich 313--231 3,073,984 1/63 Eschenbach et al 313--231 3,129,351 4/64 Martinek 219-75 X RICHARD M. WOOD, Primary Examiner.

JOSEPH V. TRUHE, SR., Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 5, 102 I I May 4, 1965 Edgar A. Bunt et al.

or appears in the above numbered pat- It is hereby certified that err he said Letters Patent should read as ent requiring correction and that t corrected below.

Column 8, line 53, for "Vehicle" red vessel Signed and sealed this 21st day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD I. BRENNER Commissioner of Patents 

